TL;DR: This page is getting a lot of views as the Win 10 deadline approaches. If you have a Dell machine, boot in safe mode or remote in via remote desktop and rename the file “C:\Program Files\Realtek\Audio\HDA\RtkNGUI64.exe”. This should allow you to boot without the blue screen.
So we rolled out the Windows 10 Fall Update (1511) to a couple of PCs at the office that were running Windows 10 RTM. Every machine appeared to upgrade fine, but once any user logged into the PC, it would throw up a frowny-face blue screen stating that “Your computer experienced a problem and needs to restart”. The “if you want to know more” reference was listed as “APC_INDEX_MISMATCH”. Searching around for this points to a driver issue, though there wasn’t really an indication of what exactly it might be.
There wasn’t enough time between the login and the blue screen to do any troubleshooting, but there were a few interesting notes:
- The PCs could stay at the lock screen or the login screen indefinitely. The blue screen only occurred AFTER logging in. This would indicate that the issue is unlikely to be a driver, as drivers would load prior to logging in.
- The blue screen appeared after login regardless of network connectivity. Wire plugged in or not, right after hitting the desktop the system would crash. The implication here is that the problem is something already on the PC as opposed to something running in the network logon script.
- All of the machines were Dell Optiplex desktops, but several different models.
Taking these items together, it would seem to point to a startup program. To test that, we could boot into safe mode (which doesn’t run startup items) and disable them. Microsoft has made it quite a bit harder to get into Safe Mode on Windows 8/10 (especially since this blue screen isn’t happening during startup, so it doesn’t trigger the repair mode automatically), but that is where we needed to turn to solve the problem.
If you aren’t familiar with getting into safe mode on Windows 10 (when you can’t get to the desktop to do it through the menu, anyway), power up the machine and wait for the Windows Logo to appear and the “busy” circle to start spinning at the bottom of the screen. Hold down the power button and shut the machine off before it boots up. Repeat this process a couple of times, and instead of the spinning busy circle, the text “Starting Automatic Repair” will appear. Let this run and you will be presented with a couple of tiles on the screen. Click on the Advanced options tile, and click on Startup Options. You will be asked to reboot again. Do so, and a startup options menu will appear. Select Safe Mode (or safe mode with networking, etc).
To solve this particular problem on our Dell machines, after booting into Safe Mode, open Task Manager, click on Details, and click on the Startup tab. We started by disabling all of the startup programs and rebooting into normal mode. This allowed us to log in without the blue screen.
After that, it was just a matter of starting each of the startup items until we hit a blue screen. The culprit for us turned out to be “Realtek HD Audio Manager”. The executable is located at “C:\Program Files\Realtek\Audio\HDA\RtkNGUI64.exe”. Running this .exe file immediately blue screens every PC we have tried it on that has the fall update installed.
I’m sure there will be an update for this eventually, but since you can’t even run updates while this error persists, it can be a real pain to get your PC back in working order. You can avoid the whole problem by disabling this startup executable prior to updating to the Windows 10 Fall Update.